1. Field of the Invention
The present invention relates in general to a three-dimensional detecting device and, more specifically, relates to an improved position detecting device having a stylus with an electrode contact at one end and an improved means for supporting the stylus.
2. Description of the Prior Art
In the use of numerically controlled (NC) machine tools, such as milling machines, grinders, drill presses and lathes, it is more and more desirable and, in fact, necessary to effect quickly and accurately three-dimensional measurements of the workpieces while in place on the machine tool, both before and after performing the specified work operation. To accomplish this, there are presently known position detecting devices that effect detection of surface positions in relation to the workpiece, as well as to actual working positions of the tool with respect to a location surface on the workpiece. An example of a known prior art detecting device is shown in FIGS. 1(a) and (b) and 2(a) and (b).
Referring then to FIGS. 1(a) and (b) and 2(a) and (b), electrode contact 11 formed as a conductive sphere is mounted at one end of elongate feeler or stylus 12. The structure for supporting stylus 12 includes housing 1, wherein the movable elements of the detecting device are contained. Specifically, three balls 2 are mounted on three thrust screws 3 having cupped ends that are arranged through the bottom of housing 1. These three thrust screws are equally spaced around a suitable diameter bolt circle. Affixed to the end of stylus 12 located inside housing 1 is a disc 4 to which is attached ring or plate 5 formed of insulating material. Attached to insulating plate 5 are receivers 6, 7, and 8, which interact with the three balls 2 mounted on supporting bolts 3. Contact is maintained between receivers 6, 7, and 8 and the respective ball 2 by means of compression spring 10, which at one end abuts the inside of the upper element of housing 1 and at the other end abuts retaining ring 9 formed of insulating material and affixed at the center of disc 4. The extent to which balls 2 are thrust into engagement with the receivers is adjustable by turning threaded screws 3. Once the proper adjustment has been reached the position of each screw 3, in relation to housing 1, is locked by means of three locking set screws 14. The position detecting device shown in FIGS. 1(a ) and (b) and 2(a) and (b) is held in a position to make position detecting measurements by means of circular shank 13, which may be held in a chuck or other tool holding device of the numerically controlled machine tool.
Operation of the position detecting device of FIGS. 1(a) and (b) and 2(a) and (b), is represented schematically in FIG. 3, wherein the shank 13 is secured in the appropriate machine tool 17, and electrode contact 11 of stylus 12 is brought into physical contact with an electrically conductive workpiece 18 that is supported by work table 15. The contact position of the stylus 12 and electrode contact sphere 11 is sensed electrically by detection circuit 16 to provide the indication of the relative location of the particular surface of workpiece 18.
In the known device, as shown in FIGS. 1(a) and (b), 2(a) and (b), and 3, receivers 6, 7, and 8 that interact with balls 2 are physically constructed to be different from one another so that each one will have only a single, three-dimensional stable position. For example, receiver 6 has an internally conical surface to receive ball 2, receiver 7 has a V-shaped groove formed therein to receive ball 2, and receiver 8 has a planar surface against which ball 2 abuts.
The known construction as described above suffers numerous drawbacks, not the least of which is the difficulty encountered when aligning or calibrating the three different kinds of receivers, in order to produce a meaningful output signal and also of the numerous parts that are involved in manufacturing and assembling this previously proposed position detecting device.